Question

The lanthanides, once called the rare earth elements, are really only "medium rare." Using noble gas and spdf notations, depict reasonable electron configurations for the following elements. (a) Samarium, Sm. This lanthanide is used in magnetic materials. (b) Ytterbium, Yb. This element was named for the village of Ytterby in Sweden, where a mineral source of the element was found.

Short answer

(a) Sm: [Xe] 4f^6 6s^2; (b) Yb: [Xe] 4f^14 6s^2.

Step-by-step solution

Understand the Electron Configuration Pattern

The lanthanides have a typical electron configuration pattern of \(Xe\), 4f, 5d, 6s. This means they follow the noble gas configuration up to the element Xenon (Xe) and then fill the 4f, 5d, and 6s orbitals.

Determine Samarium's (Sm) Electron Configuration

Samarium (Sm), with an atomic number of 62, follows the Xenon configuration, then fills the 4f orbitals before moving to 5d and 6s. The configuration is: \[\text{Sm:} \ [Xe] \, 4f^6 \, 6s^2 \] Here, the 4f orbital is partially filled with 6 electrons, and the 6s orbital has 2 electrons.

Determine Ytterbium's (Yb) Electron Configuration

Ytterbium (Yb), with an atomic number of 70, fills its electrons in the same pattern as Sm but fills the 4f orbital completely. The configuration is: \[\text{Yb:} \ [Xe] \, 4f^{14} \, 6s^2 \] In this case, 4f is fully occupied with 14 electrons and 6s with 2 electrons.

Key concepts

Lanthanides

The lanthanides are a fascinating group of elements often called the rare earth metals. Despite their name, they are not as rare as they seem. These elements are found in the f-block of the periodic table and include 15 elements from lanthanum (La) to lutetium (Lu). Lanthanides are well-known for their shiny appearance and are often used in various applications, such as manufacturing powerful magnets, phosphors for color television tubes, and catalysts in petroleum refining. Their unique properties arise mainly from the filling of the 4f orbitals, which we will learn more about later.

Samarium

Samarium, symbolized as Sm, is an important lanthanide element with an atomic number of 62. One of samarium's most notable uses is in the creation of high-performance materials like samarium-cobalt magnets, which are very strong and resilient to heat and corrosion. This makes them ideal for use in motors and headphones. Samarium has a typical electron configuration that follows the noble gas configuration of xenon (Xe). After xenon, electrons occupy the 4f orbitals. For samarium, this configuration is \[\text{Sm:} \ [Xe] \, 4f^6 \, 6s^2 \]. It has 6 electrons in the 4f orbitals, contributing to its unique chemical properties.

Ytterbium

Another intriguing member of the lanthanide series is ytterbium, represented by the symbol Yb and atomic number 70. Ytterbium has several applications, especially in electronics and materials science. It is used as a dopant in optical materials and for improving the grain refinement of stainless steel. Ytterbium differs from some of its lanthanide peers because its 4f orbitals are fully occupied. The electron configuration for ytterbium is similar to other lanthanides up to the xenon noble gas core, after which it fills its 4f sublevel entirely: \[\text{Yb:} \ [Xe] \, 4f^{14} \, 6s^2 \]. This full 4f sublevel leads to unique characteristics and uses.

Noble Gas Notation

Noble gas notation is a shorthand way of writing electron configurations that provides several conveniences. It involves using a noble gas symbol in square brackets to represent the core electrons of an element. This approach simplifies the electron configuration by focusing only on the outer electrons involved in chemical bonding. For example, the core electron configuration for both samarium and ytterbium can be denoted by xenon \([Xe]\) since both elements build on the electron configuration of xenon. This notation makes it easy for chemists to identify and compare lanthanide and other elemental configurations quickly without writing out long sequences of electron shells.

4f Orbitals

The role of the 4f orbitals is crucial in understanding the chemistry of the lanthanides. These orbitals can hold up to 14 electrons, as seen in the configuration of elements like ytterbium. The filling of the 4f orbitals in lanthanides begins after the 5s, 5p, and 6s shells have been occupied. The 4f orbitals are less shielded from the nucleus, which means that their electrons are more tightly bound compared to outer d and s orbitals. This tight binding influences both the physical properties, such as magnetic behavior, and chemical reactivity of the lanthanides. For example, samarium's partially filled 4f orbitals lead to unusual magnetic properties harnessed in advanced technologies.